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SDPL 2001Notes 4: Intro to Stylesheets1 4. Introduction to Stylesheets n Discussed recently: –Programmatic manipulation of (data-oriented) documents n Now a more human-oriented point of view: –How to specify formatting or rendering of structured documents? n Concepts, properties and requirements of style systems on a general level –later examples of concrete style languages (CSS, XSL)
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SDPL 2001Notes 4: Intro to Stylesheets2 Introduction to Style Sheets (Based on Brüggemann-Klein, A., Wood, D., Electronic Style Sheets. Universität Freiburg, Institut für Informatik, Bericht 45, Januar 1992.) n Declarative markup of structured documents indicates purely syntactic structure –no semantics (processing, formatting, …) n Electronic style sheets –specify layout and appearance of document content –e.g. FrameMaker templates, Word styles, or LaTeX style files; CSS and XSL style sheets
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SDPL 2001Notes 4: Intro to Stylesheets3 Style Sheets? n In traditional publishing –a set of rules about diction and language for some manuscript n Electronic style sheets –deal with graphical layout of documents (In near future aural properties, too?) –setting and changing of properties controlling layout and appearance of document content –define a mapping from documents (structure+content) to external representation on a presentation medium (paper, screen, audio, …)
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SDPL 2001Notes 4: Intro to Stylesheets4 Why Style Sheets? n Separation of content and presentation is a basic "dogma" in structured documenting –supports longevity and multi-use of documents –(unnecessary complication for single-purpose and single-use documents) n Relationship between documents and style sheets is many-to-many –single style for many documents »supports manageability (of, say, consistent look and feel of a corporate Web site) –many styles for a single document »supports multiple output media (print, different Web clients, hand-held-devices, …)
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SDPL 2001Notes 4: Intro to Stylesheets5 Tasks of a Style Sheet n Style sheet guides the transcription process –translating descriptive markup into formatter input (stream of formatting commands and text) –input a document tree of typed elements and symbolic cross references n Formatter is a device (program) capable of –hyphenation (breaking of character sequences) –typeface attribution (characters into glyphs) »e.g, single glyph fi for " fi" –line breaking (assembling glyphs into lines) –page breaking (lines into pages)
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SDPL 2001Notes 4: Intro to Stylesheets6 Process of Transcription
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SDPL 2001Notes 4: Intro to Stylesheets7 Process of Formatting n Creates a detailed description of presentation
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SDPL 2001Notes 4: Intro to Stylesheets8 Process of Rendering n Display/play the document on output medium
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SDPL 2001Notes 4: Intro to Stylesheets9 Style Rules n Entries of a style sheet n Attach transcriptions to logical elements n Most style rules in practise structure-based –associated to instances of element types in the structure tree n Also grammar-based style rules –associated to occurrences of element types in the document grammar
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SDPL 2001Notes 4: Intro to Stylesheets10 Transcription types 1. calls of parameterised formatting tasks 2. automatic numbering 3. generation of text 4. rearrangement of elements n Application of transcriptions can depend on element context
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SDPL 2001Notes 4: Intro to Stylesheets11 Context Specification (1) n General rule –semantically equivalent structures (instances of the same element type) should be formatted identically n Exceptions (due to conventions, aesthetics, etc) –paragraphs indented, except the first one –heading numbers 1, 2, … in body vs. A, B, … in appendices –author lists in references (‘‘ Aho et al. ’’ vs ‘‘ Aho and Ullman ’’) –indication of target element type ( Table, Figure, Section,...) for cross references
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SDPL 2001Notes 4: Intro to Stylesheets12 Context Specification (2) n Need access to ancestors, siblings, descendants, targets of cross references n Context conditions by a context predicate –Boolean expression built of »a reference to the current element »functions like parent, leftSibling, leftMostSibling, children, and ref n Rule applied if the context condition is true n Context specification orthogonal to transcription types (Cf. XPath expression language in XSL)
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SDPL 2001Notes 4: Intro to Stylesheets13 Parameterised Formatting Tasks n The most common transcription type: n set formatting characteristics of subelements –typeface attribution (for strings or inline-elements) –line breaking (for paragraphs or blocks) –page breaking (for documents) –parameterized by type size, line length, indentation, margins… hierarchy of elements hierarchy of nested formatting tasks hierarchy of nested presentation areas hierarchy of elements hierarchy of nested formatting tasks hierarchy of nested presentation areas
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SDPL 2001Notes 4: Intro to Stylesheets14 Numbering n Different schemes –consecutively through document »same numbering sequence possibly common to a set of element types (e.g., for theorems and examples) –nested numbering for, say, nested lists »relative to occurrences of another element type higher in document hierarchy n often via named counters with a start value and a scope
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SDPL 2001Notes 4: Intro to Stylesheets15 Derived or Inserted Content n boilerplate text –text not present in the source document –e.g., letter headings, © marks, bullets, … n textual content inserted at the beginning or at the end of the current element n table of contents, indexes –need to specify the source of included material
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SDPL 2001Notes 4: Intro to Stylesheets16 Subelement Rearrangement n Examples –reverse the order of titles and authors in references –sorting of the reference list »requires functions operating on textual contents n Subelement suppression a special case n Not supported by the weakest style systems
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SDPL 2001Notes 4: Intro to Stylesheets17 Viewpoint on Style Languages n Next we'll have a look at CSS, and later at XSL –How do the discussed concepts appear in the languages? –How do the languages support these general requirements?
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